Deep Brain Stimulation (DBS) is becoming an acceptable therapeutic modality in neurosurgical treatment of patients suffering from chronic pain, Parkinson's disease or seizure, and other medical conditions. Other electro-stimulation therapies have also been carried out or proposed using internal stimulation of the sympathetic nerve chain and/or spinal cord, etc.
One example of a prior art DBS system is the Activa® system from Medtronic, Inc. The Activa® system includes an implantable pulse generator stimulator that is positioned in the chest cavity of the patient and a lead with axially spaced apart electrodes that is implanted with the electrodes disposed in neural tissue. The lead is tunneled subsurface from the brain to the chest cavity connecting the electrodes with the pulse generator. These leads can have multiple exposed electrodes at the distal end that are connected to conductors which run along the length of the lead and connect to the pulse generator placed in the chest cavity.
Functional MRI is an imaging modality that can be used to evaluate cardiac, neurological and/or other disorders. It may be desirable to use MRI for patients with implanted stimulation devices and leads. However, currently available lead systems may be unsuitable to use in a magnetic resonance imaging (MRI) environment. For example, the devices may not be MRI compatible, i.e., they may contain ferromagnetic materials, which may distort the MRI images. Also, currently available lead/probe/cable systems may be susceptible to unwanted induced RF and/or AC current and/or localized heating of the tissue. For example the Medtronic Activa® device recommends that MRI imaging be carried out in a 1.5 T magnet without using body coils, i.e., only using head coils for transmission of the RF excitation pulse(s). Also, the problem of unwanted RF deposition may increase as higher magnetic fields, such as 3 T systems, become more common for MRI imaging (the RF pulses having shorter wavelengths).
It is believed that the clinical outcome of certain medical procedures, particularly those using DBS, may depend on the precise location of the electrodes that are in contact with the tissue of interest. For example, presently, to treat Parkinson's tremor, the DBS probes are placed in neural tissue with the electrodes transmitting a signal to the thalamus region of the brain. However, it has been reported that in about 30% of the patients implanted with these devices, the clinical efficacy of the device/procedure is less than optimum. This may be attributed to the inaccurate/imprecise placement of the lead/probe/electrode with respect to the cranial or neural tissue.
Other non-MRI applications, such as RF/microwave diathermy treatment, can use leads that employ an alternating current to cauterize tissue. The diathermy alternating current delivered during the therapy can be in the range of between about 1 KHz-350 MHz. In certain situations, the lead system may undesirably act as an antenna, picking-up and depositing current in localized tissue where the leads are exposed, thereby potentially increasing the SAR or specific absorption rate (a way of measuring the quantity of radiofrequency (RF) energy that is absorbed by the body).
Notwithstanding the above, there remains a need for alternative medical lead configurations.